Fe-Mn Hydroxides Research Articles

Deposit potential and distribution of cobalt and nickel in the sludge of chromite placer mining process at Nui Nua ultramafic massif area, Thanh Hoa province, Vietnam

Chromite placer is widely distributed in Quaternary sediments located around the Nui Nua ultramafic massif in Thanh Hoa province, Vietnam. The long-term mining works targeting chromite placer in this area have left a huge amount of waste sludge, up to tens of millions of tons. The paper aims to introduce a deposit potential and distribution of cobalt- and nickel- bearing minerals within the waste sludges generated from the chromite placer mining operations around the mines situated near the Nui Nua ultramafic massif in Thanh Hoa province, Vietnam. Based on field investigations and sample analyses, two groups of waste sludge have been identified: clay-sized sludges and debris waste sludges. The former group is plastic bentonite clay, distributed in depressions and low terrain, and has low contents of cobalt (0.06%) and nickel (0.67%), which is of impractical significance for the recovery purposes of cobalt and nickel. The latter group is usually distributed in relatively high terrain, forming waste sludge ranging from several thousand to hundreds of thousands of tons in volume. These deposits include rock fragments, mineral fragments derived from the Nui Nua ultramafic massif, along with dark spherical nodules rich in goethite, limonite, and Fe-Mn hydroxides, which contain relatively high contents of cobalt (up to 0.75%) and nickel (up to 2.43%) in the waste sludge and chromite placer mines. The cobalt and nickel are mainly concentrated in Fe-Mn nodules made up of goethite, limonite, todorokite, and other Fe-Mn hydroxides. Data from chromite placer explorations, combined with the study results, provide reliable insights into the distribution of cobalt and nickel resources within the waste sludges and chromite placer deposits in the Co Dinh area (northeast of Nui Nua ultramafic massif) and Mau Lam (southwest of Nui Nua massif), Thanh Hoa province. A preliminary estimation of potential resources of Co and Ni metals have been made for the debris waste sludges at Co Dinh and Mau Lam areas based on the ratios of debris particles in the sludges and their contents of Co and Ni along with published resources and reserves of chromite placer ores.

Enrichment pattern of tungsten in sediments under methane seepage environments: Applicability as a proxy for tracing and reconstructing (paleo-)methane seepage

The release of hydrogen sulfide by sulfate-driven anaerobic oxidation of methane (SD-AOM) during methane seepage activities has a strong impact on the evolution of marine redox conditions and the cycles of redox-sensitive elements (e.g. Mo and U). Consequently, the sedimentary enrichment or depletion of these elements is often used to trace and reconstruct (paleo-)methane seepage activity. In recent years, tungsten (W) has shown promise as an indicator of marine redox changes, but its applicability to trace methane seepage activity is unknown. This study identified significant differences in the W content of sediments in methane seepage environments compared to suboxic environments not influenced by methane seepage and oxic environments in the South China Sea. The sediments subjected to methane seepage were characterized by low W contents, similar to those of euxinic Black Sea sapropels. It is believed that the sulfidic environment resulting from SD-AOM is the primary cause of W depletion in sediments subjected to methane seepage. By examining W's interaction with its twin element, Mo, we present WMo enrichment patterns in various environments. In methane seepage environment (sulfidic environments), sediments had high MoEF (> 10) and low WEF (< 2) with a high Mo/W molar ratio (> 10); in suboxic environments not influenced by methane seepage, sediments exhibited a WMo enrichment pattern similar to the UCC (the MoEF and WEF values are predominantly below 1 and 2, respectively, with a low Mo/W molar ratio, <1.5); in oxic environments (enrichment of FeMn (oxy)hydroxides), sediments exhibited high MoEF (2 < MoEF < 10) and high WEF (> 2), with a medium Mo/W molar ratio (1.5–10). This further indicates that the Mo/W molar ratio has great potential in tracing and reconstructing (paleo-)methane seepage activities.

Platinum-bearing Fe-Mn oceanic crust on basalts: mineralogy and model of formation

Fe-Mn oceanic crust on basalts of the guyot in the Mid-Pacific Seamount (Pacific Ocean, depth 2486 m, chemical composition (wt %): Mn 24.2, Fe 12.6, Ni 0.59, Co 0.72, Cu 0.13; (ppm) Pt 0.35, Pd 0.0052), was studied using 3D-technology of mineralogical research. In addition to dominaiting vernadite and goethite, the following minerals are identified in the hydroseparation (HS) concentrates of the crust: 1) rock forming and accessory minerals of basalts (clinopyroxene, plagioclase, potassium feldspar, biotite, ilmenite, titanomagnetite, Ti-chrome spinel, zircon, apatite); 2) sulfides that are identical to those from the basalt substrate (pyrite, chalcopyrite, bornite, chalcocite, tennantite, nickel pentlandite Ni4S3, sphalerite, galena, argentite/acantite, molybdenite); 3) native metals (iron, nickel, copper, titanium, tungsten); 4) iron silicides (gupeiite Fe3Si, xifengite Fe5Si3, and hapkeite Fe5Si3); 5) platinum group minerals - unnamed (Cu,Pt)4Si and rustenburgite (Pt,Pd)3(Sn,Sb). The complexes of ore minerals in basalts are identical to those of the Fe-Mn crusts. Basalt accessories are assumed to be primary phases and a source of metals for the formation of native minerals. “Microdroplets” of native iron Fe, (Fe,Ni), nickel Ni, (Ni,Cr), (Ni,Fe) and copper Cu (sizes 20–100 microns, degree of sphericity up to 100%) represent the products of their crystallization from metal melts in basalts, transported by deep fluid into Fe-Mn crusts on these rocks. The zoned microglobules of 20–70 microns sizes with iron or native nickel (core) + successive rims of wüstite-magnetite and Fe-Mn hydroxides were identified. They were apparently formed during the movement of these solid microparticles (from bottom to the top) along intergranular spaces and other permeability channels in basalts under conditions of increasing oxygen fugacity and falling temperature at various levels of deep fluid infiltration. The crystallization of native metals in the Fe-Mn crust that are characterized by low-temperature (10 °C) and oxidizing (fO2 MHG magnetite-hematite-goethite) conditions of mineral formation is impossible. The goethite replacement to different extent of many grains of relict Fe-minerals (sulfides and native metals) that are “foreign” to the Fe-Mn crust have been established. Fe-Mn crusts were formed as a result of the precipitation of colloidal particles Mn2+(Ba2+и Sr2+), to a lesser extent of the iron hydroxide Fe(ОН)3, as well as the concentration and transformation of micrograins of minerals of other metals, extracted by fluid from basaltic substrates. The comparison of the physico-chemical parameters of crystallization of basalts and native metals suggests another source of formation of native minerals in basalts, different from the postmagmatic basaltic fluid, i.e. deep-seated sharply reducing "hot" gas flows associated with superplumes. The mineralogical data determines a volcanogenic-fluid-oceanic model for the formation of Fe-Mn crusts on underwater oceanic elevations.

Extracting paleo-weathering signals from authigenic phases in lake sediments: A case-study of Lake Baikal

Authigenic phases in lake sediments hold the potential to record changes in the isotope compositions of past lake water, potentially yielding valuable information on secular changes in continental weathering patterns and rates, including over past glacial cycles.Here, different leaching approaches are investigated with the aim of extracting Sr, Nd, Pb, and Be hosted in authigenic Fe-Mn (oxy)hydroxide sediment phases for precise isotope measurements. Elemental Al/Mn, Ca/Mn, and P/Mn ratios obtained via a mild reductive leach agree well with the composition of marine authigenic Fe-Mn phases. For core top sediments, leached Sr isotope compositions obtained with this leach agree well with the composition of lake water. The Be and Nd isotope compositions of core top leachates are consistent with the spatial variability observed in the water column. Due to high concentrations in Fe-Mn phases, leachate compositions are dominated by authigenic Be, Sr, Nd, and Pb, even in cases when as much as 40% of leached phases (by mass) are non-authigenic. These lines of evidence suggest that the mild reductive leach successfully extracts the modern lake isotope composition from modern sediments in terms of the isotope systems investigated. We further show that the leaching method is also reliable for older sediments (<340 ka): leached paleo-Sr isotope compositions are consistent between the current and previous interglacial periods, as well as for glacial periods. This suggests that reconstructed water isotope compositions are not affected by early diagenetic processes, instead reflecting environmental factors around the lake that determine the composition of weathering fluxes. Although more difficult to assess for Be, Nd, and Pb due to the heterogeneity of modern lake water, the data we present indicate the overall robustness of the leaching approach.These promising results open up lakes as archives for paleo-weathering reconstructions. Given that marine reconstructions face some important limitations (e.g., integration of basin-wide changes in weathering processes, long residence times for Sr, etc.Fe), lake records provide an avenue to improve our understanding of changes in regional weathering processes over glacial-interglacial timescales. The mild reductive leach used here may also be useful for meteoric Be studies in marine shelf settings, to prevent leaching of terrestrial sedimentary Fe-Mn oxy(hydroxide) phases.

Characteristics of iron-manganese nodules containing nickel and cobalt in chromite deposits in Co Dinh, Thanh Hoa province

Along with the chromite ore bodies, very early on, geologists recorded the presence of cobalt (Co) and nickel (Ni) metal. The resource of cobalt and nickel is forecasted with over 3 million tons of Ni and over 260 thousand tons of Co metals. Until now, however, knowledge about the existence form and distribution of Ni and Co in chromite ore bodies is very limited. Researching the sludge in the chromite mines and in comparison with manganese nodules found in the ocean floor helps to detect the presence of particles of iron and manganese (Fe-Mn nodules) in granular sewage sludges and in primary chromite ore bodies. Fe-Mn hydroxides, including todorokite mineral, are believed to be the adsorption medium and forming of Ni and Co in the Co Dinh placer chromite. Determining the existence form and distribution of Ni and Co in chromite placer deposits has scientific and practical significance in sampling orientation, sample processing, geological exploration, and reserve and resource estimations, sorting and recovering technology of Co and Ni metals.

Geochemical Characteristics of Trace Elements and REEs and their Geological Significance for Uranium Mineralization within the Qianjiadian Sandstone-Hosted Uranium Deposit, Songliao Basin

The Qianjiadian uranium deposit is a typical interstratified oxidized zone sandstone-hosted uranium deposit hosted in the Upper Cretaceous Yaojia Formation of the southern Songliao Basin. Despite its significance, little research has been conducted on the relationship between trace elements, REEs, and uranium mineralization in this deposit. This study presents new geochemical data from sandstones in the oxidation, transition, and reduction zones. The sandstones in the transition zone are highly enriched in U and moderately enriched in Mo, Cd, and V compared to those in the oxidation and reduction zones. They are also weakly enriched in Co, Ni, and Zn. The oxidation and transition zone sandstones have higher ∑LREE and ∑HREE contents than those in the reduction zone. However, the oxidation zone sandstones are characterized by LREE enrichment and flat HRRE distribution, while the transition zone sandstones show HRRE enrichment and flat LREE distribution. These trace element and REE differentiation characteristics within each subzone are closely related to the geological process of interstratified oxygenation. Oxygenated uranium-bearing fluids from southwestern provenance areas carried multiple trace elements and REEs and infiltrated along the oxidation sandstones to reach the Yaojia Formation’s transition zone. During this process, a certain amount of Mo, V, Cd, and LREE from the oxygenated ore-forming fluids was precipitated by Fe-Mn hydroxide adsorption or calcite and siderite cementation. Meanwhile, about 20.33% of preexisting U in the oxidation zone sandstones was continuously extracted and entered into the oxygenated ore-forming fluids. In the transition zone, where dissolved oxygen was exhausted and hydrocarbons were continuously injected, U, Mo, Cd, V, Co, Ni, Zn, and REEs were unloaded and precipitated as uranium minerals, sulfide minerals, or carbonate minerals. The enrichment of Mo, Cd, V, and HREEs in the sandstones can serve as new prospecting indicators for the Qianjiadian uranium deposit.

Gross Alpha-Particle Activity and High 226Ra Concentrations Do Not Correspond with High 210Po in the Atlantic and Gulf Coastal Plain Aquifers of the United States

210Po, which is of human-health concern based on lifetime ingestion cancer risk, is indirectly regulated in drinking water through the U.S. Environmental Protection Agency’s gross alpha-particle activity (GAPA) maximum contaminant level of 15 pCi/L (picocuries per liter). This regulation requires independent measurement of 226Ra for samples exceeding the GAPA screening level of 5 pCi/L. There is no such requirement for 210Po. Co-occurrence of 226Ra and 210Po, alpha-emitting 238U-decay-series progeny, might be helpful in locating high-210Po waters but is unverified. Relations among 210Po, 226Ra, and GAPA evaluated for samples from 257 public-supply wells from Coastal Plain aquifers showed that concentrations of 226Ra correlated with GAPA but neither correlated with 210Po concentrations. The highest concentrations of 226Ra and 210Po were found under differing geochemical conditions. The highest 226Ra occurred in low-pH oxidizing waters and in neutral-pH reducing waters, where geochemical conditions render Fe–Mn-hydroxide sorbents inefficient. 210Po was highest (10.1 pCi/L) in reducing waters with high pH (>7.5, which results from progressive cation exchange), where 226Ra was lowest─exchanged to clay minerals. Because 226Ra and 210Po did not co-occur, the GAPA screening might not be protective for 210Po. Independent 210Po analysis is prudent, especially where groundwater is reducing with high pH and low 226Ra concentrations.

Characteristics and Causes of High-manganese Groundwater in Pearl River Delta During Urbanization

The high concentration of iron and manganese in groundwater is harmful to human health, and the sources of manganese in rapidly urbanization areas are complex. Based on more than 2500 sets of hydrochemical data in different historical periods, the spatial distribution characteristics, sources, and genesis of groundwater manganese in different aquifers and areas with different urbanization levels in the Pearl River Delta were studied by using mathematical statistics and principal component analysis. The results showed that the concentration of manganese in groundwater in the pore aquifer was obviously higher than that in the fissure and karst aquifer. The proportion of high-manganese groundwater in the pore aquifer was twice that in the fissure and karst aquifer. The proportion of high-manganese groundwater in urbanized and suburban areas was significantly higher than that in non-urbanized areas. On a regional scale, the decomposition of organic matter and the reductive dissolution of Fe-Mn (oxygen) hydroxide in sedimentary strata under reductive conditions may have been the main factors controlling the increase in manganese concentration in pore aquifers. High-manganese groundwater in fissured aquifers may have been affected by low-oxygen domestic sewage leakage accompanying urbanization and industrial wastewater leakage and infiltration accompanying industrialization. The pore high-manganese groundwater was controlled by reduction conditions, and the weakly acidic environment of fissure and karst high-manganese groundwater was the important influencing factor. In the past 10 years, the groundwater environment in the study area has been improving, and the increase in groundwater redox potential and pH was not conducive to the formation of high-manganese groundwater, which was also the main cause of the overall decrease in Mn2+ concentration in groundwater of different types of aquifers in the process of urbanization.

Mercury (Hg) geochemistry of mid-ocean ridge sediments on the Central Indian Ridge: Chemical forms and isotopic composition

To geochemically characterize mercury (Hg) in the deep-sea ridge environment, the total concentration, chemical forms (sequential leaching extraction), and isotopic compositions of Hg in surface sediments from the middle portion of the Central Indian Ridge were investigated. Highly elevated Hg concentrations (up to 13,000 ng/g) in sediments near the hydrothermal vent are associated with intense hydrothermal activity driven by serpentinization. The hydrothermal impact on these sediments is also evident in the REECN fractionation pattern with a remarkably strong positive europium (Eu) anomaly. Most volcanic and hydrothermal Hg in the study area is preferentially precipitated with sulfides; in the hydrothermal vent area, however, scavenging by Fe-Mn hydroxides is another significant removal pathway of Hg. Thus, such precipitation and production of sulfides and hydroxides are a major cause of local enrichment of Hg around the mid-ocean ridge. Most sediments show limited or no mass-independent fractionation (Δ199Hg = +0.02 ± 0.21‰, 2σ, n = 15), indicating that syngenetic magmatic or mantle-derived materials are the dominant Hg source. However, the large variation in mass-dependent fractionation was observed, especially in the vent-distal sediments (δ202Hg = −1.10 ± 0.80‰, 2σ, n = 11), which occurred mainly during the formation of the sulfides and may be associated with preferential precipitation of lighter isotopes. Our study demonstrates that an off-axis high-temperature hydrothermal system driven by exothermic serpentinization of ultramafic mantle rocks may serve as a significant Hg source and provides further insights into grasping the behavior of hydrothermal and volcanogenic Hg in active deep-sea ridge systems.

Characterization of Geochemistry in Hydrothermal Sediments From the Newly Discovered Onnuri Vent Field in the Middle Region of the Central Indian Ridge

The recently discovered Onnuri hydrothermal vent field (OVF) is a typical off-axis ultramafic-hosted vent system, located on the summit of the dome-like ocean core complex (OCC) at a distance of ∼12 km from the ridge axis along the middle region of the Central Indian Ridge (CIR). The plume chemistry with high methane anomaly was consistent with the precursor of hydrothermal activity; however, the fundamental characteristic of the OVF system, such as the hydrothermal circulation process and source of heat, remains poorly understood. Here, we focus on the geochemical features of surface sediments and minerals collected at and around the OVF region in order to better understand this venting system. The results reveal that the OVF sediments are typified by remarkably high concentrations of Fe, Si, Ba, Cu, and Zn, derived from hydrothermal fluid and S and Mg from seawater; depleted C-S isotope compositions; and abundant hydrothermally precipitated minerals (i.e., Fe–Mn hydroxides, sulfide and sulfate minerals, and opal silica). Notably, the occurrence of pure talc and barite bears witness to strong hydrothermal activity in the OVF, and their sulfur and strontium isotope geochemistry agree with extensive mixing of the unmodified seawater with high-temperature fluid derived from the gabbroic rock within the ultramafic-dominated ridge segment. The findings reveal that the OVF is a representative example of an off-axis, high-temperature hydrothermal circulation system, possibly driven by the exothermic serpentinization of exposed peridotites. Given the widespread distribution of OCC with detachment faults, furthermore, the OVF may be the most common type of hydrothermal activity in the CIR, although the paucity of data precludes generalizing this result. This study provides important information contributing to our understanding of the ultramafic-hosted hydrothermal vent system with a non-magmatic heat source along mid-ocean ridges.

Oxidative degradation of p-chlorophenol by the persulfate-doped Fe-Mn bimetallic hydroxide, the parametrical significance, and systematical optimization.

Aqueous Fe(II)-catalyzed activation commonly deteriorates the oxidation performance of persulfate (PS) to the treatment of organic contaminants. In this study, a PS-doped layered bimetallic hydroxide (Fe-Mn hydroxide) was synthesized to construct a heterogeneously catalytic system to solve the issue brought by homogeneity. The molar ratio of Fe(II) to Mn(II) and the mass ratio of PS to Fe-Mn hydroxide both had a significant impact on the catalytic degradation of p-CP. Reaction temperatures engaged in the most essential role in influencing the degradation and removal of p-chlorophenol (p-CP). The optimal combination of factors for the preparation of PS-hydroxide and the treatment of p-CP was finally determined by significance analysis. The degradation process was appropriately fitted by the pseudo-first-order kinetic model. The benzene ring in p-CP was broken by PS-hydroxide during the adsorption. The surface modification of PS-hydroxide caused by the valence transition of Mn was beneficial to the adsorption and catalytic degradation of p-CP.

Lead compounds in bottom sediments of the Seversky Donets floodplain

Investigations on heavy metals in water bodies are extremely important in a comprehensive assessment when the anthropogenic activities disturb the natural environment. The present paper studies the composition of Pb compounds in highly contaminated bottom sediments of a natural settling basin of a chemical plant at the Atamanskoye lake in the floodplain of the Seversky Donets River by sequential fractionation. The predominance of the residual Pb fraction, which is represented by layered silicates (hydromuscovite, montmorillonite, kaolinite) is shown. Organic matter and Fe-Mn (hydr)oxides also play an important role in metal interaction. High mobility of Pb is noted, which associated with imposing high environmental risks in the studied area.

Association of metals with geochemical phases in wetland soils of a Ramsar site in India.

Mobilization of metals in wetland ecosystems is a function of the behaviour of a specific metal species and is dependent largely on the prevailing micro-environmental conditions. Apparently, five different chemical forms of metals are known with varying affinity to binding sites, mobility, bioavailability and toxicity. Quantification of these forms of metals in the soils is imperative in predicting their biogeochemical fate and toxicity. In this context, we examined the association of Cu, Pb and Zn, with various geochemical phases in the soil profile of wetland system of Keoladeo National Park, a Ramsar site in India. The assessment covered the soil profile until 100cm depth at every 25-cm intervals. Different operationally defined geochemical phases in the soil at different depths were examined during the study for respective metal concentrations. Hydrous oxides of Fe-Mn were the major carrier for all the three metals and the fraction associated with exchangeable phase was the least. The low organic matter content in the soil seems to be influencing the metal association with the organic matter (OM-S) phase, which was also a less preferred carrier for metals. For Cu (5.8-78.4%) and Pb (33.5-88.5%), Fe-Mn hydroxide phase was an important binding site and for Zn (31.02-79.03%), it was the silicate mineral matrix (RES phase). This suggests the importance of micro-environmental conditions in the wetland bed such as redox and pH in mobilization of metals. As metals such as Pb have high eco-toxicological potential, an assessment of fractional concentrations of metals provides insights into their mobility and bioavailability in aquatic ecosystems. This aids wetland managers to develop appropriate strategy to maintain quality of inflow water, the single most crucial factor for a wetland ecosystem, and thus controls the micro-environmental conditions.

Speciation the heavy metals; Fe, Mn, Cu, Zn, Ni, Cd and Pb in the Sediment of Lake Burullus (Ramsar site), Egypt

This study was carried out to investigate the speciation and distribution of the heavy metals; Fe, Mn, Cu, Zn, Ni, Cd and Pb in the sediments of Lake Burullus, Egypt. The mean metal concentrations of the sediments followed the order of Fe >Mn> Zn > Cu > Ni >Pb> Cd. The evaluated contamination with these metals was revealed moderate to strong ecological risk. According to applying index of the potential ecological risk index (RI), risk assessment code (RAC) and modified risk assessment code (mRAC); the risk levels showed the following order Cd = Pb>Mn> Ni > Zn > Cu > Fe. Considering the metals speciation, high levels were found in the residual fraction for Fe, Cu, Zn and Ni; while were in Fe-Mn hydroxide fraction for Cd and Pb, and in carbonate fraction for Mn. All metals showed enrichment during summer at stations of the southeastern parts of the lake due to the heavy discharge of contaminants from shakhloba, kotichener and Hoksa drains. Therefore, monitoring of contaminants discharge and determination of heavy metal and other pollutants in the water and sediments and its fractionation at Lake Burullus should be introduced for future and management strategies.

Spatial distribution and environmental geochemistry of zinc metal in water and surficial bottom sediments of Lagoon Burullus, Egypt

Lagoon Burullus is located in the North West quadrant of the Nile Delta. It receives drainage water through several drains around the lagoon. Understanding the mobility and bioavailability of zinc metal in bottom sediments of Lagoon Burullus is essential for the design of remediation processes and the institution of environmental recommendation for zinc pollution.Single extractions used to fractionate zinc into five fractions. The chemical analyses preceded using atomic absorption spectrometry after using the digestion technique. Zinc concentrates in the residual fraction (167.5μg/g) followed by the organic (14.6μg/g), exchangeable (3.2μg/g), carbonate (2.4μg/g) and then the Fe-Mn hydroxides (1μg/g) fractions. The average content of zinc (189μg/g) is about three fold the average earth's crust.Ecological pollution index show that the metal has a low-risk assessment to surrounding ecosystem. The anthropogenic activities considered as the main source of pollution.

Arsenic Environmental Threshold Surpass in Estuarine Sediments: Effects of Bioturbation.

We investigate the distributions of the metalloid arsenic (As) and metals iron (Fe) and manganese (Mn) in the sediments of two pristine areas of a biological reserve in the Patos Lagoon Estuary. This area is occupied by Spartina alterniflora and by Neohelice granulata crab colonies and low concentrations of As are expected. The bioturbation/bioirrigation of sediments by crabs and the roots of plants lead to the penetration of oxygen below the oxic/suboxix division and the subsequent precipitation of Fe-Mn hydroxides. Ferruginous incrustations and nodules along roots and crab channels propagate to depths of over 35cm and sediment contains up to 33mg kg- 1 of As. The metalloid distribution in sediments is strongly correlated with that of Fe but not with Mn. This study revealed that areas with biologically disturbed sediments could demonstrate contamination in As, which is not anthropogenic in origin.

Intraplate volcanic-hydrothermal systems of the Clarion-Clipperton zone, Pacific Ocean

The results of recent studies of specific craterlike structures in sediments of the Clarion-Clipperton zone (CCZ) of the Pacific Ocean are summarized. It was established from the example of a crater located in the bottom area with age of ∼40 Ma that such craters from several hundreds of meters to a few kilometers in diameter and from 15 to 100 m deep are a result of evolution of intraplate volcanic-hydrothermal systems mostly active in the CCZ area beginning from the Middle Miocene. Vertical chimneylike channels from a few centimeters to 0.5 m across in pre-Middle Miocene carbonate sediments in the areas of subvolcanic basaltic stocks with an age of 16–18 Ma and less are the structural elements of these systems. The channels are filled with nontronite clays and Fe-Mn hydroxides, which are the products of discharge of low-temperature hydrotherms. New data have allowed us to reach a conclusion on the origin of thermal convection of volcanichydrothermal systems, which dissolved the host carbonate sediments and formed the craterlike structures at the final stage of evolution.

주요 황사발원지 토양의 지구화학적 특성 및 미량원소 존재형태 연구

본 논문에서는 황사 발원지 (타클라마칸, 알라샨, 오도스 사막 및 황토고원) 토양 시료의 지구화학적 특성을 규명하고, 이들이 지표환경과 인체에 미치는 영향을 알아보고자 하였다. 중국 건조지역에서 채취한 토양 시료 내 주원소 함량의 공간적 변화는 각 지역별로 크지 않았으며, 이는 각 지역 내 토양이 오랜 기간 동안 바람에 의해 균질하게 혼합된 것으로 해석된다. 한편 미량원소의 경우에는, 시료 채취 지점에 따라 미약한 함량의 차이를 나타낸다. 이들 중 Cr, Cu, As, Co, Ni, V, Y, Sc, Sn, Pb, Zn, Cd, Cs, Li, Th, U 등은 원소 간에 서로 양의 상관관계를 보이며, 이들의 특성은 황토고원과 다른 사막 (타클라마칸, 알라샨 및 오도스 사막) 토양에서 뚜렷하게 구분된다. 모든 사막 및 황토고원 토양의 Fe의 지구화학적 존재형태는 대부분 "잔류형 (85% 이상)"으로 나타났으나, Mn 및 Ca의 존재형태는 사막에 따라 존재형태의 차이가 현저하게 나타났다. Mn은 황토고원 토양에서는 "산화철망간광물 수반형 (55.4%)"이, 그리고 타클라마칸 사막에서는 "탄산염광물 수반형 (33.8%)"이 다른 사막 토양에 비해 2-5배 높게 나타났다. 또한 Ca의 경우에는 타클라마칸 및 알라샨 사막 토양에서 "탄산염광물 수반형"이 각각 75.9% 및 50.5%로 높게 나타났으나, 황토고원 (6.6%)과 오도스 사막 (2.1%)에서는 낮게 나타났다. 사막 및 황토고원 내 미량원소의 이동도를 기준으로 이들 미량원소를 5개의 그룹으로 분류하였으며, Cd, Pb 및 Cu의 이동도가 각각 87%, 33% 및 30% 이상으로 나타났다. 따라서 사막 및 황토고원 내 Cd, Pb 및 Cu는 지표수 등과 반응하였을 때 쉽게 용해되어 지표환경 및 인체 건강에 악영향을 줄 가능성이 있음을 지시하고 있다. In this study, we investigated the chemical characteristics of soils collected from the several deserts and loess in China known as the typical source areas of Asian dust (the Taklamakan desert, the Alashan desert, the Ordos desert and the Loess Plateau). Based on our analysis, we examined the possibility of adverse effects on environments and human health. In each desert and loess, major elemental compositions of soils did not show large variations, implying that the long-periodic mixing of soils in each area made their chemical compositions homogeneous. Minor elements of soils in each desert and loess showed more complicated patterns with strong correlations each other (e.g., Cr, Cu, As, Co, Ni, V, Y, Sc, Sn, Pb, Zn, Cd, Cs, Li, Th, U). These results thus enable us to discriminate the soil of the Loess Plateau from those of the other deserts in China. The results of sequential extraction experiments for soils showed that the chemical speciation of Fe was dominant in residual fraction (>85%) in all deserts and loess, but the fractions of Mn and Ca chemical speciations were very different in each area. In the case of Mn, the fraction of amorphous Fe-Mn hydroxides (55.4%) in the Central Loess Plateau and the carbonate fraction (33.8%) in Taklamakan desert were higher as much as 2 to 5 times than other deserts. The chemical speciations of Ca are dominant in carbonate fraction in Taklamakan (75.9%) and Alashan (50.5%) deserts, but carbonate fractions of Ca in the Loess Plateau and Ordos deserts were low (6.6% and 2.1%, respectively). According to the mobility of trace elements inferred from the results of sequential extraction procedure, we could classify them into five groups, and the mobility of Cd, Pb and Cu are more than 87%, 33% and 30%, respectively. Therefore, Cd, Pb and Cu in soils of deserts and loess could be easily dissolved when interacted with surface water. As such, they could give adverse effects on surficial environments and human health.

Heavy metals (Cr and Ni) distribution and fractionation in cropland soils from reclaimed tidal wetlands in Pearl River estuary, South China

Abstract Heavy metal contamination was compared for soils with different land use (cropland and wetland) in the reclaimed region of the Pearl River estuary. A sequential extraction technique was used to produce five chemical fractions (exchangeable (F1), carbonate (F2), Fe–Mn hydroxide (reducible) (F3), organic (F4) and residual (F5)) to study the effects of reclamation and tillage on the distribution and mobility of the heavy metals Cr and Ni. The results revealed that generally the contamination levels increased with a longer history of reclamation (100> 40> 30> 10 years) whilst an undisturbed reference wetland was least affected. The most substantial quantities of both Cr and Ni were observed in the residual fraction, which may be a consequence of the mixing effects of soil tillage and planting. With the exception of the 20-30 cm layers from the wetland and 10 year old cropland samples, the total concentration of Cr and Ni at all sites and all soil layers exceeded the moderately polluted level according to the SQGs of the US EPA.

Occurrence and paragenesis of diagenetic monazite in the upper Triassic black shales of the Marvast region, South Yazd, Iran

Upper Triassic-Jurassic black shale at Marvast, Iran, contains grey to green-grey ellipsoidal nodules of monazite ranging from 0.1 to 2 mm across. The presence of host-rock mineral inclusions within the monazite grains, low Th content in the monazite, lack of relict yellow cores (characteristic of igneous monazite), and the absence of monazite in the other sedimentary sequences in the Marvast area rule out a detrital origin for the monazite nodules and suggest authigenic crystallization during sediment compaction. Enrichment of the cores of the monazite grains in mid-range to heavy rare-earth elements (REE) and their rims in La + Ce point to variations in the degree of REE mobility and/or evolving composition of the diagenetic mineralizing fluid during nodule growth. The phosphorus and REE required for monazite crystallization were probably derived from seawater and adsorbed on clays and Fe-Mn hydroxides. The interstitial fluids expelled from the sediments during burial compaction and diagenesis became enriched in P and REE through complexing. The association of the Marvast monazite nodules with the black shale may indicate that organic complexes aided in the mobilization and transport of the REE into the pore fluids. Detailed field investigations in the study area and vicinity show that authigenic monazite in the upper Triassic-Jurassic shale sections is spatially associated with quartz lenses. It is likely that these lenses are surface expressions of shallow intrusive magmas, which provided the heat that promoted the mobilization and redistribution of the REE and P, and initiated precipitation of monazite in the overlying sediments.